Typically, air bag systems are employed in vehicles as a safety device for protecting the driver and passengers during a collision. Sensors, stimulated during vehicle collisions trigger the air bag to expand between a driver and a steering wheel and/or between a passenger and the instrument panel of the vehicle. Therefore, the impact of the collision is absorbed into the air bag, securing the safety of the driver and passenger.
During an accident or collision, a vehicle's speed decelerates. A deceleration detector detects the deceleration and provides a signal to a microcomputer. The microcomputer determines an impact degree of the vehicle according to the detected deceleration signal. The microcomputer analyzes the collision waveform generated during the collision. If the degree of the deceleration is more than a set value, an air bag driving unit is activated and explodes nitrogen gas, thereby, expanding the air bag.
One drawback of the typical air bag system is that the microcomputer operates the air bag driving unit using only the deceleration signal provided by the deceleration detector. Therefore, the typical air bag system does not consider deviation in different types of collisions or degrees of movement and a deformation degree of the vehicle from the collision. The deviation in collisions can actually affect an expansion time of the air bag, such that the air bag is expanded to early or too late. As a result, the driver and the passengers are subject to a dangerous condition when the deceleration reaches the maximum value.
Additionally, a required expansion time of the air bag, or required time to fire (RTTF), which is required for appropriate expansion of the air bag at the moment of the collision, is applied to the conventional air bag system. The RTTF is directly linked with the expansion of the air bag and is an important factor in the evaluation standard when the stability and performance of the air bag system are tested.
The following are generally applied to the test for evaluating the expansion performance of the air bag. A collision test in which a vehicle collides with a wall of 0° to 30° at a speed of 8 mph (mile per hour) to 35 mph. A collision test in which a vehicle collides with a pillar at a speed of 19 mph to 30 mph, and a test in which a vehicle is crushed under another vehicle (e.g., a truck or a large-sized bus).
In collision tests where a vehicle is collided head-on with a pillar at 19 mph the minimum expansion time of the air bag is roughly 53 ms (milliseconds), and a maximum expansion time of the air bag is roughly 82 ms. The RTTF has an actual standard time of 50.2 ms. Therefore, as is determined and shown by collision tests, the conventional air bag system has a large derivation in the air bag expansion time and can greatly exceed the RTTF.
In collision tests where a vehicle is collided with a truck or a large-sized bus at a speed of 20 mph and is crushed under the truck or the large-sized bus the minimum expansion time of the air bag is roughly 0 ms, and a maximum expansion time of the air bag is roughly 79 ms. The RTTF has an actual standard time of 48.7 ms. Therefore, as can be seen from the collision waveform measured in actual collision tests, the expansion time of the air bag according to the convention air bag system is greatly variable and unstable.
Therefore, it would be advantageous to have an air bag control system and method that deployed the air bag at the appropriate time in response to a variety of collisions.